1. Field of the Invention
The present invention relates to a cooler of an exhaust gas recirculating system, as well as to an exhaust gas recirculating system including one such cooler.
Partly recirculating the exhaust gas to the fresh air end of the engine has been known in engine design for a long time as a means of reducing noxious emissions. Whilst this makes it necessary to cool the exhaust gas as a function of the operating condition of the engine, it is especially at low engine temperatures and/or low engine loading that cooling the exhaust gas may be undesirable. This is why, for this purpose a bypass is usually provided to bypass the cooler, the extent of the exhaust gas flow through the bypass or cooler being regulated by a suitable valve means.
2. Prior Art
A cooler is known from DE 197 33 964 A1. This cooler comprises a housing including coolant inflow and outflow ports. Furthermore provided is a bypass pipe which bypasses the cooler such that the recirculated exhaust gas flows at least in part through the bypass pipe and is not cooled.
The invention is based on the object of providing a cooler of an exhaust gas recirculating system as well as an exhaust gas recirculating system equipped with such a cooler for a simplified system and cooler structure.
In accordance therewith it is provided for that the bypass pipe arranged within the housing is now integrated to a certain extent in the housing of the cooler, i.e. running therein. In other words, the housing of the cooler comprising coolant inflow and outflow, more particularly the so-called shell of the cooler, forms the outer envelope of the cooler. Only the coolant inflow and outflow ports in the region of the cooler are provided outside of the housing, but not the bypass pipe which is instead integrated in the housing or shell. This substantially simplifies the structure of the cooler, resulting in the cooler being designed less complex. More particularly, the cooler now has a pleasing compact configuration with its surroundings uncluttered by additional piping, such as, for example, the bypass pipe formerly provided separately therefrom.
Tests have indicated that the wanted effect, namely practically avoiding cooling of the exhaust gas flowing through the bypass pipe, can already be achieved by configuring the bypass pipe significantly different than the cooling pipes. Although due to integratation in the shell of the cooler, within which the coolant, for example water, is located, achieves a certain cooling of the bypass pipe and its flow, this cooling effect may be maintained relatively slight by providing a single bypass pipe with a sufficient cross-section as extending substantially straight through the cooler. Contrary thereto, the portion through which the exhaust gas flows for the purpose of cooling can be configured so that it comprises a plurality of branched and correspondingly smaller pipes surrounded by a flow of coolant to achieve the desirable cooling effect. In accordance therewith, the cooling pipes, as compared to the bypass pipe, can be extended, for example by configuring them coiled. Now, when the exhaust gas flows through the cooling pipes, adequate cooling is achievable, whilst when the flow passes through the bypass pipe, even though this is located within the cooler shell, the cooling effect is substantially eliminated.
Preferred embodiments of the invention are set forth in the further claims.
It is good practice generally to configure the bypass pipe thermally insulated so that the cooling experienced by the bypass pipe is relatively slight. One particularly preferred embodiment is formed by the bypass pipe being provided as a double-walled pipe, the cavity between the two walls producing the desired insulating effect.
In this arrangement particularly good results have been achieved by forming a vacuum between the two walls of a double-walled pipe to eliminate, in particularly, the convection effect of a medium located between the two walls of the pipe. Furthermore, this embodiment lends itself particularly well to an advantageous method of producing the cooler in accordance with the invention, by the bypass pipe and preferably the complete cooler being produced by vacuum brazing. In this procedure the solder xe2x80x9ctrapsxe2x80x9d the vacuum between the two walls of a double-walled bypass pipe to thus enable, with no extra complication in production, a substantially insulated bypass pipe to be fabricated, suitable for integrating in the housing of the cooler in accordance with the invention whilst substantially preventing cooling of the exhaust gas flowing through the bypass pipe when in use.
As regards the exhaust gas inflow and outflow ports of the cooler in accordance with the invention, it is basically conceivable that the cooler features separate inflow and outflow ports at at least one end. In this case the exhaust gas flow would be branched off already prior to attaining the cooler, and depending on the setting of an actuator the exhaust gas would then attain the inflow of the cooling pipes or bypass of the cooler before being subjected to cooling or not. In this case a single outflow could be provided at the downstream end of the cooler since the porting as described could still join within the cooler. As an alternative it is, of course, just as conceivable that two outflows are provided, the flow paths then joining downstream of the cooler. Furthermore, an actuator may be provided at the downstream end of the cooler. In this case the upstream end of the cooler could feature one or two inflows, depending on whether the exhaust gas flow has already been branched or not upstream of the cooler. In any case, in this embodiment is can also be assured by an actuator at the end of the cooler that the closed off flow path is in all cases filled with exhaust gas, but not with a throughflow so that, for example, should the bypass pipe be closed off at the end thereof, the cooling pipes receive the throughflow in achieving cooling of the exhaust gas. Irrespective of the conceivable embodiments as described it is currently preferred in the scope of the invention that the cooler comprises at least one single inflow and preferably, in accordance therewith, a single outflow. To separate the flow paths, i.e. the bypass pipe, on the one hand, and the cooling pipes, on the other, an actuator is integrated to advantage in the cooler which serves to close off at least the bypass pipe. It is to be noted that the actuator may be provided basically so that it closes off optionally the bypass pipe or the cooling pipes or the common inflow of several cooling pipes. Tests have indicated, however, that especially in a suitable arrangement of the bypass conducive to flow, satisfactory results can be achieved when only the bypass pipe can be closed off by the actuator. In other words, the bypass pipe is closed off to achieve a throughflow of the cooling pipes and thus cooling of the exhaust gas. When the bypass pipe is opened, most of the exhaust gas flows through the bypass pipe whilst a relatively small proportion of the exhaust gas continues to flow through the cooling pipes. Measurements have shown that in this arrangement the exhaust gas is likewise slightly cooled, of course. For certain applications the difference between the cooling extent in this case and the extent of the cooling when the bypass pipe is closed and throughflow is only via the cooling pipes is sufficient for influencing the temperature of the recirculated exhaust gas.
As regards the actuator preferably integrated in the cooler in accordance with the invention one advantageous embodiment consists of the actuator being a flap. This flap may be either pivoted at one end such that it closes off the bypass pipe or the inflow to the cooling pipes in two different positions. As an alternative, the flap may be configured in the form of a throttle valve, pivoted in a middle portion so that, for example, only the bypass pipe is closed off when it is not a mandatory requirement to close off the cooling pipes as described above.
A single actuator solely provided for closing off the bypass pipe is sufficient especially in preferred embodiments in which the cooler comprises a sole inflow for the exhaust gas to be recirculated, and the bypass pipe, as viewed flow-technically, is incorporated in the extension of the inflow so that it constitutes the xe2x80x9cpath of least resistancexe2x80x9d for the exhaust gas in flowing through the bypass pipe, this meaning, more particularly, that when the inflow is arranged centrally, then also the bypass pipe is arranged centrally. In other words, the bypass pipe, just like the surrounding cooling pipes, are configured to port a so-called ported plate that the exhaust gas directed into the cooler, for a relatively low flow resistance, arrives at the opening, downstream of which the bypass pipe is located so that a substantial proportion of the exhaust gas flows therethrough. Contrary to this, when cooling is desirable and the bypass pipe is closed off by the actuator, the exhaust gas arrives at the closed opening and thus flows through the parallel arrangement of the cooling pipes. The same effect can also be achieved, however, by the embodiment in which the bypass pipe is not located centrally in the cooler but at its rim, by the inflow in this case being configured inclined such that the exhaust gas flows initially inclined, substantially in the direction of the bypass pipe, into the cooler so that it constitutes the path of least resistance with the bypass pipe open in flowing therethrough. This too, makes a relatively simple actuator, merely closing off the bypass pipe, sufficient. Otherwise, in this case the cone as evident in the Figures (cf. FIGS. 3 and 4) porting the inflow of the cooler, would be configured inclined such that the desired flow in the direction of the bypass pipe, located at a rim, is assured. It is to be noted again that in accordance with a preferred embodiment the actuator is provided such that it closes off only the bypass.
The diameter of the cooler in accordance with the invention, more particularly of its shell, can be maintained relatively small, the required cooling effect being achieved when the bypass pipe is disposed substantially centrally in the housing. When this arrangement is combined with a substantially centrally inflow, the favorable flow conditions can be assured which, as described above, involve merely closing off the bypass when the exhaust gas is to be cooled, whereas if the cooler is to be bypassed and the bypass pipe is opened, the cooling pipes can remain open.
Even though the cooler in accordance with the invention is a separate component of an exhaust gas recirculating system, it is provided for in accordance with the invention that a complete exhaust gas recirculating system is provided, comprising the cooler in accordance with the invention in one of the embodiments as described above.
It is to be noted in conclusion that the invention may also be viewed as a method in which the bypass pipe is integrated in the housing, more particularly, the shell of a cooler. In this arrangement the bypass pipe is configured as a double-walled pipe and at least the bypass pipe, preferably the complete cooler is fabricated by vacuum brazing.
This permits achieving the advantage that the vacuum between the two walls of the double-walled bypass pipe is conserved by the solidified solder and that the bypass pipe can be configured thermally insulated at very little expense.